I wouldn't bother coming south to look for one. I live in Southwest Mississippi and I've had to go elsewhere to find one. While I did not pay $500 for a used one, I did pay significantly more than I really thought one was worth to get a good used one. Just not a lot of them around and even the ever present Marlin 30-30 lever gun is going for more than $250 around here...if it's in decent shape, anyway.
I guess if you just stumbled across someone with a clean Marlin 375 for sale who was in a rush to sell it you might get it for under $400, but you'd have to get really lucky or live in an area where they sold a lot of them so that there were a number of good used ones for sale to help keep the price in line.
Anyway, that's my experience in looking for one for the past 6 months for what that's worth.